Mechanical instability of normal and aneurysmal arteries
Introduction
Rupture of abdominal aortic aneurysms (AAA) is the thirteenth leading cause of death in the United States (Vorp, 2007). Extensive biomechanical studies have shown that highly elevated local stress and weakened aneurysm wall make aneurysms vulnerable to rupture (Fillinger et al., 2002, Fillinger et al., 2003, Vorp, 2007, Rodriguez et al., 2008).
Aneurysms are often associated with vessel tortuosity (Hatakeyama et al., 2001, Wolf et al., 2001, Fillinger et al., 2004, Vorp, 2007). For example, in patients with Loeys–Dietz syndrome, the carotid and cerebral aneurysms tend to be tortuous (Loeys et al., 2006, Johnson et al., 2007). Around 10% of Loeys–Dietz syndrome patients also have abdominal aortic aneurysms, which may become tortuous as well (Wolf et al., 2001, Johnson et al., 2007). It has been suggested that artery tortuosity may lead to aneurysm formation (Deterling, 1952, Arends et al., 2008) and aneurysmal tortuosity has been proposed as a risk factor for aneurysm rupture (Del Corso et al., 1998, Sacks et al., 1999, Fillinger et al., 2003, Pappu et al., 2008, Rodriguez et al., 2008, Georgakarakos et al., 2010). Therefore, it is important to better understand the relation between artery tortuosity and aneurysms.
Recent studies from our lab suggested that artery buckling, the loss of mechanical stability due to hypertension, decreased axial stretch ratio and elastin degradation in the wall, can lead to vessel tortuosity (Han, 2007, Han, 2009a, Lee et al., 2012, Han et al., 2013). However, the mechanical stability of aneurysmal arteries and the post-buckling behavior of normal and aneurysmal arteries have not been investigated. Therefore, the objective of this study was to investigate the buckling and post-buckling behavior of normal and aneurysmal arteries and the effects of buckling on the wall stress in aneurysmal arteries.
Section snippets
Methods
The effects of aneurysms on arterial stability were evaluated by simulating the buckling and post-buckling behavior of normal and aneurysmal arteries using finite element analysis. Simulation results were compared with theoretical estimations and experimental measurements of porcine carotid arteries for validation.
Material constants of porcine carotid arteries
The convex material constants for the set of six normal porcine carotid arteries and one artery treated with elastase are given in Table 1. The pressure deformation curves obtained using the convex material constants fit the experimental data well (Fig. 2). The critical buckling pressures determined from the FEA simulations, using the convex material constants, also demonstrated good agreement with the critical buckling pressures (Fig. 2) determined from the theoretical buckling equation (Han,
Discussion
In this study, we investigated the buckling and post-buckling behavior of normal and aneurysmal arteries with fusiform aneurysms. Our results demonstrated that the lateral deflection of arteries increased nonlinearly with increasing lumen pressure post-buckling. The presence of aneurysms could reduce the critical buckling pressure of arteries, and buckling resulted in higher axial stresses in the aneurysm wall. In addition, the shape of aneurysms affected the critical buckling pressure. For
Conflict of interest statement
The authors have no conflict of interest.
Acknowledgments
This work was supported by CAREER award #0644646 from the National Science Foundation and grant R01HL095852 from the National Institutes of Health. It was also partially supported by HHSN 268201000036C (N01-HV-00244) for the NHLBI San Antonio Cardiovascular Proteomics Center. Avione Lee was partially supported by a MBRS-RISE pre-doctoral fellowship under grant GM60655 from NIH. We also thank the Computational Systems Biology Core funded by NIH (G12MD007591) for providing access to their
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These authors contributed equally to this work.